Growers interested in growing strawberries on a plasticulture system can choose to use plug plants or bare-root plants. The pros and cons of using each of the planting materials was discussed in a previous article. This article will discuss the importance of planting dates for growers who chose to use plug plants.
In the 2020-2021 season, the strawberry plasticulture trial at Southwest Purdue Agricultural Center reached the highest yield of the past three seasons. The highest yielding variety was Rocco that yielded 2 lb/plant. Besides Rocco, Flavorfest, Chandler, and Liz also yielded over or close to 1.5 lb/plant. This yield was much higher than yields of previous seasons, in which, yields of even the best varieties were less than 1 lb/plant. Fall and winter in the 2020-2021 season are in general, good for strawberry production. Another important factor that I think makes a substantial difference in the yield is the planting date. Strawberry plugs were planted on Aug. 24 in 2020, while they were planted on Sep. 11 in 2019. There was about two weeks’ difference. Although two weeks does not sound like an enormous difference, it could significantly impact the plant growth in the fall and the yield in the following spring. I will use growing degree days (GDD) to explain the impact.
Growing degree day is calculated by daily mean temperature minus a base temperature. Since strawberry crown growth and development are best at temperatures above 50°F, 50°F was used as the base temperature in the GDD calculation. Figure 1 is the accumulated GDD from planting to the end of February in the past two seasons (2019/2020 and 2020/2021). From Aug 24 (planting date in 2020) to Sep 11 (planting date in 2019), there was about 500 GDD accumulation in 2020, which was close to one-third of total GDD accumulation from Aug. 24 to the end of Feb. What this tells us is that delaying planting for two weeks from August to September could sacrifice one-third of GDD accumulation in the fall.
Figure 1. Accumulated growing degree days from planting to end of February in 2019-2020 and 2020-2021 strawberry season.
Strawberry crown growth in the fall is in a short window in our region. After the middle October, plant growth reduces tremendously. Therefore, it is extremely important for growers who are interested in using plug plants and grow strawberries in a plasticulture system to plant them as early as possible. When I first started to work on the plasticulture system a few years ago, strawberry plugs are only available in Sep. and Oct. This works well for growers in the southern states. But it is too late for our region. The good news is that with more nurseries are selling strawberry plugs in the temperate regions now, it is possible to get plugs as early as the middle of August. Our experiment in southern Indiana showed that with early planting of plug plants, appropriate variety selection, and plant care, it is possible to achieve a decent yield for growing strawberries in a plasticulture system.